With US troops advancing on Baghdad, BBC News Online looks at what they can expect to find in the Iraqi capital.

Baghdad, home to five million Iraqis and nerve centre of the Iraqi regime, stretches along both banks of the river Tigris. It is a sprawling city spread across some 150 square miles.

It is a city of contrasts - of rich residential districts in the centre of city and over-crowded, predominantly Shia Muslim slum neighbourhoods.

One such area is Saddam city, a suburb to the north-east of the capital. It is home to some two or three million Shia - many of whom resent the ruling regime. It is seen by analysts as the area of the city that could most welcome the downfall of Saddam Hussein.

The main presidential palace on the banks of the Tigris

Cutting through the city are six-lane motorways ideal for tank movement, but these soon give way to narrow alleyways that could draw troops into hand-to-hand combat.

There have been fears that Saddam Hussein would try to turn this ancient city into a "Mesopotamian Stalingrad" - a reference to the siege of Stalingrad, one of the bloodiest battles of World War II.

It is from Baghdad that the Iraqi leader has wielded power over the country for over two decades, with the help of elite troops, and intelligence and security agencies.

The main body in charge of protecting the regime's power base in the capital is the Special Republican Guard (SRG), who are among the country's most disciplined and loyal troops.

Symbols of power

Many of the important symbols of the regime's power - including lavish presidential palaces - are concentrated on the west bank of the Tigris, in the heart of the city.

One area, some two miles long and almost entirely walled off, is home to a number of government compounds. It is know as the Mujamma Dijla - the Tigris compound - and houses the Revolutionary Command Council, the main leadership, and two presidential palaces.

Close by are the information ministry, the president's official residence, Baath party HQ and Republican Palace. All are reported to have been hit during recent bombing raids.

The Shia Muslims of the sprawling suburb of Saddam City are largely resentful of the regime

Underneath many of these government buildings is a labyrinthine system of bunkers. One such bunker is believed to house a vast underground command centre with an elaborate network of strong rooms beneath tonnes of reinforced concrete and steel.

Besides military and political buildings, the centre of the city is also home to what could be seen as symbolic targets by coalition forces. The Victory Arch, a gigantic structure of Saddam Hussein holding two swords, celebrates "victory" in the Iran-Iraq war, according to the government.

The site of coalition tanks driving along the wide boulevard alongside the arch could have symbolic significance, as it is here that the Iraqi leader has held his massive military parades.

Old city

Eleven bridges connect the two halves of the city. Coalition troops will likely see these as strategic, as seizing control of the bridges, the main one being Jumhuriya (Republic) bridge, will cut the city in two.

The older parts of the city, made up of narrow alleyways, lie on the eastern bank of the Tigris. These could provide cover for Iraqi fighters and draw coalition troops into hand-to-hand combat.

This is something US commanders are anxious to avoid, although some US troop divisions have been equipped with battering rams, grappling hooks, folding assault ladders and battle axes, in anticipation of breaking down doors and scaling rooftops to root out Saddam Hussein's forces.

The city's sprawling southern suburbs, a sea of box-like concrete homes and massive government buildings, could also provide cover for thousands of Iraqi soldiers.